Abdominal aortic
aneurysms (AAA) occur in more than 10 000 people each year in the United States
(Park, Park, Kim, Cho, Ahn, & Jae, 2015). 
According to Wadgaonkar, Black, Weihe, Zimmerman, Fishman, and Johnson
(2015), “an abdominal aortic aneurysm is a pathological dilation of the
abdominal aorta to more than 3 cm in the greatest diameter”.  A prompt diagnosis is imperative.  Without it, the disease will advance and if
untreated can result in serious health issues and often death (Baker, Atlas
& Afendulis, 2008).  A mortality rate
of 75-90 percent is expected when an AAA ruptures and the correct treatment is
not administered (Park et al., 2015).   It is critical that an accurate diagnosis is
made and a precise evaluation of the state of the AAA is obtained (Park et al.,
2015).  Many image modalities can be used
to diagnose an AAA but computed tomography angiography (CTA) is the favoured
imaging modality of choice (Taheri, Haghighatkhah, Pourghorban & Hosseini,
2013).   A CTA requires an intravenous injection of
contrast media and therefore patients must be screened for a previous history
of a contrast allergy (Furlow, 2012). 
Patients with a previous mild allergy must be pre-medicated and those
with a severe allergy will have to use an alternate modality for diagnosis
(Iyer, Schopp, Swanson, Thapa & Phillips, 2013).

Comparison
of Methods to Diagnose an AAA

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Ultrasonography (US),
magnetic resonance imaging (MRI), conventional radiography and computed tomography
(CT) are image modalities used to diagnose an AAA (Park et al., 2015).  An ultrasound is often used since it a cost effective
test to perform and is a suitable means to check the enlargement of a blood
vessel (aorta) (Park et al., 2015).  See
Figure 1.  Park et al., (2015) further
explains ultrasound imaging is used to diagnose an AAA because it is
non-invasive which means it requires no needles or injections.  It is readily available at most hospitals and
does not use any ionizing radiation (Park et al., 2015).  However, patients’ body habitus (obesity) and
intestinal gas can compromise the visualization of the aorta in an US exam
(Anderson, 2001).  Another technique to
diagnose an AAA is the use of CT with the administration of contrast media called
computed tomography angiography (CTA) (Baker et al., 2008).  See Figure 2. 
This procedure is more invasive than ultrasound because it requires the
patient to have contrast media injected intravenously in order to visualize
arteries, blood vessels and tissues (Furlow, 2012).  With the use of CT technology and contrast
media, image data of these structures can be reconstructed into 2 dimensional
(2D) and 3 dimensional (3D) representations (Furlow, 2012).  See Figure 3. 
Unlike US, CT provides information about the nearby vascular anatomy and
structures and this is information is necessary for treatment planning
(Anderson, 2001).  Magnetic Resonance
Angiography (MRA) is also another method to diagnose an AAA (Anderson, 2001).  See Figure 4. 
Studies done comparing the results of MRA with CTA scans have shown MRAs
to be a concrete method of diagnosis (Anderson, 2001).  Anderson (2001) also states, MRI scanners are
very expensive and are restricted in availability.  MRA to visualize an AAA is also invasive
because it requires an injection of Gadolinium (Anderson, 2001).  Patients with metal clips, pacemakers or
other metallic devices are unable to have a MRI.  These drawbacks do not make MRI the best
choice for an AAA diagnosis (Anderson, 2001). 
Conventional angiography is an interventional radiographic procedure in
which a catheter is used to the injected contrast media into the aorta to
diagnose an AAA (Baker et al., 2008). 
See Figure 5.  This procedure is
very invasive and has high rate of complications that could be
life-threatening, such as an embolus becoming lodged and blocking the blood
vessel (Baker et al., 2008).  CTA has the
ability to validate the precise extension of the aneurysm (Taheri et al.,
2013).  The accuracy of
determining an AAA using CT is about 90 percent which is high compared to US,
which has an accuracy of 80 percent (Park et al., 2015).  As CTA is becoming the method of choice to
diagnose an AAA, in the future it may fundamentally replace conventional
angiography (Taheri et al., 2013).   Therefore, a CTA is the gold standard for the
detection of an AAA due to its high accuracy, quick image acquisition,
availability and demonstration of surrounding anatomy (Taheri et al., 2013).   

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